Eight British children have been born via mitochondrial replacement therapy

The healthy baby boy's mother carried genes for a rare mitochondrial disease called Leigh syndrome and after multiple miscarriages the family opted to try the controversial procedure. It was conducted by a US doctor in Mexico. The procedure is prohibited in the United States.

This primer video dives into the science of mitochondrial disease risks, how this controversial mitochondrial replacement technique can work, and why proponents say this reproductive advance—already legalized in the UK and Australia—is needed in the United States.

Columbia University researchers created four embryos using mitochondrial replacement therapy for four female patients who didn't want to pass on mitochondrial diseases to their children. Yet US law restricts the researchers from implanting the embryos so they remain frozen.

It was the second country, after the UK, to legalize the procedure, which is still prohibited in the US. There are more than 300 rare mitochondrial diseases that can be passed from a mother to her offspring.

An agency committee assessed if this approach could have undesirable ripple effects across multiple generations and whether a clinical trial involving this approach would be appropriate. As of 2026, the US has continued to prohibit this procedure though it is legal in other settings including the UK and Australia.

Though the topline promise of this approach is avoiding passing on mitochondrial diseases, some researchers and companies have been eyeing its potential for helping with female infertility, since faculty mitochondria may contribute to the condition. Recent research suggests this approach could be promising.

Women who are carriers of mitochondrial diseases that wish to have children without those conditions cannot be biological parents without three-parent IVF. The alternatives are to adopt or have a child via egg donation.

The process scoops out about 99% of the mother's mitochondrial DNA—replacing it with that of a donor woman—but because that roughly 1% is still in the system there is still a small chance of disease for the resulting child or future generations.

Mitochondrial replacement therapy can be conducted with four different techniques, with varying genetic material transferred depending on the approach. Maternal spindle transfer, one common method, involves transplanting the nuclear DNA from a mother into an unfertilized egg from a donor. The donor egg is then fertilized and implanted into the mother's uterus using in vitro fertilization. Another major approach, pronuclear transfer, does the genetic swapping after the mother's egg has already been fertilized. This order of operations may be uncomfortable for some individuals, but the success rate with this technique is higher.

This 2022 academic presentation from Stanford University's Dr. Gregory Enns offers a detailed overview about mitochondrial therapy approaches. Enns, a pediatric geneticist, explains how well-functioning mitochondria support the human body.

Gynecologist Patrick Steptoe and his collaborator Robert Edwards, a biologist, attempted to fertilize a human egg cell in a petri dish 101 times before finally succeeding. This resulted in the birth of Louise Brown—at the time referred to as a "test tube" baby—in 1978, who was born into the spotlight.

Pregnancies involving three kids or more have dropped 62% from 1998 to 2023, a trend that the Centers for Disease Control and Prevention links to fewer embryo transfers during assisted reproduction procedures—a transition prompted by more refined techniques and technical advances. Though multiple births can occur naturally, often pregnancies involving multiple births have been the result of efforts to ensure pregnancy success by transferring multiple embryos.

From refined artificial insemination and microsurgical sperm extraction to experimental uterine transplants, scientific innovation is rapidly advancing potential fertilization technologies. But they come along with costly trials, some ethical dilemmas, regulatory issues, and more.

In 2022, 251,542 patients tried assisted reproductive technologies—most commonly IVF—resulting in more than 98,000 infants. Those children represent around 2.6% of the babies born in the US.

Roughly 1,000 to 4,000 kids are born with these conditions each year in the US though many of the diseases are fatal. Mitochondrial disorders often affect the organs that require the most energy, including the heart, brain, and muscles.

Ethical concerns with this controversial procedure include that a little bit of a child's offspring would be from a third person and that the decisions made with this pregnancy will affect numerous generations, making a permanent change to the gene pool.

In 2023, researchers at UC Davis performed the first-ever fetal stem cell transplant, attempting to cure a case of spinal bifida prior to childbirth using stem cells derived from the placenta. The trial, and others including an effort to treat muscular dystrophy, highlight the potential power of stem cell therapy.

Some critics of this approach worry that any genetic manipulation will both culturally and technologically normalize the idea of "designer babies"—embryos that are manipulated or selected based on physiological characteristics including height, eye color, athletic ability, and intelligence.

KJ Muldoon had a 50% chance of surviving a genetic mutation until doctors developed a one-of-a-kind gene-editing therapy. In an interview with one of the researchers behind the treatment, learn what it will take to make personalized genetic medicine possible for everyone.

The Alabama Supreme Court's 2024 ruling that embryos created through IVF are legally children has had a chilling effect on the fertility industry. A few centers for reproductive assistance paused egg fertilization, and others are questioning where the legal argument will lead. The decision has some surprising implications for the future of IVF technology, including techniques that haven't yet been invented.

This reproductive technology is available across the US, but if states take action to prohibit the discarding of unused embryos or pass related legislation, it could affect access to IVF. Laws prohibiting IVF or effectively outlawing the procedure by defining personhood as being conferred at the moment of conception have been under discussion in several states in recent years, including Ohio, Virginia, and Texas.

Researchers at a hospital in the US have successfully used artificial wombs to care for preterm lambs and are now looking at the possibility of human trials. This nine-minute video includes interviews with the researchers and explains the reasoning...

Using stem cells from skin and mouth cells could save hopeful parents time and money and spare egg donors from significant amounts of discomfort throughout the process. There are potential consequences, not just for infertility treatment, but for the ability to create customized cells of any type.

The field offers hope to thousands of families annually, but it is also largely unregulated, and for a small number of parents, things can go terribly wrong.

The four healthy girls were delivered by cesarean section and joined a larger family that includes their parents and a 2-year-old older brother. Without the use of fertility drugs, quadruplet births are rare, but the chances are even slimmer that they'll be sets of identical twins. Medical professionals say the odds are around one in a million.

In spite of its wide acceptance as a form of reproductive assistance today, and its role in helping millions of people have children, in vitro fertilization was once considered a controversial threat to society. One magazine went as far as to describe the procedure as "the biggest threat since the atom bomb."

Gene editing via CRISPR could theoretically fix many issues in biology, but editing the mitochondrial genome has remained challenging. In recent years, there has been some progress reaching these cellular powerhouses.

The non-identical twins, who would also be half-siblings, result from a rare biological phenomenon called heteropaternal superfecundation. Britain's first known twins with different dads, featured in this article, learned of each other's existence in recent years, when they were both 45. They discovered each other after taking DNA tests from Ancestry, a genealogy company.

Artificial wombs may be able to help preterm babies survive their early entry into the world and possibly curb the long-term adverse health effects associated with such premature birth. This article dives into the current ethics and science behind artificial wombs and ectogenesis, which is when a fetus develops in artificial conditions.

Victoria Gray was the first patient to receive a CRISPR-based therapy, which eliminated her symptoms and restored her health. The therapy's initial cost of $2.2M has kept it out of reach of many patients.

A look at the companies offering surrogacy to the ultrarich—including Chinese men taking their reproductive cues from Elon Musk.

Scientists are working to create artificial wombs that would help preterm babies survive their early entry into the world. But how much help could this technology provide, and how much of a problem are preterm births? This article details some of...

The child, born in May 2020, was selected by her parents to optimize for certain health qualities based on an analysis of her multifactorial genes by a New Jersey-based company called Genomic Prediction. Her embryo was selected for implantation based on polygenic risk scores for heart disease, diabetes, and cancer.

Though their use for embryo selection is illegal in many locations, private clinics in the US may offer polygenic scores to inform embryo selection. The US Food and Drug Administration has not banned their use—instead the tests are regulated like supplements, meaning they are not regulated before they come to market but consumers can file complaints and then the agency may take action.

Known as the Star system—for Sperm Track and Recovery—it uses artificial intelligence to help identify and locate "hidden" sperm in men with a rare infertility condition called azoospermia. The condition affects about 1% of men, and these individuals have sperm counts low enough that the individual spermatozoa in their ejaculate may be undetectable. In late 2025, the first baby was born after the child's parents used this assistive technique to locate sperm.

While birthing twins has been a rare occurrence for humans, research suggests that twins were actually the norm much further back in primate evolution. It’s proposed that single-childbearing turned out to be critical for the evolution of larger babies with larger heads. Discover more about the shift that gives insight into primate evolution.

Scientists have used the technique to create embryos from eggs harvested from captive southern white rhinos and implanted into a southern white rhino. They hope to use this proof of concept to eventually use IVF to revive the population of northern white rhinos, which are extinct in the wild and have no living males left, using a precious reserve of frozen embryos and a surrogate southern white rhino mother.

An 18th-century Russian woman gave birth to 69 children through 27 pregnancies, with an unbelievable 16 pairs of twins, seven triplets, and four quadruplets.

Recent research has explored potential links between increased childhood cancer occurrence, particularly leukemia, and assisted reproductive technology (ART). Though some studies have detected this type of association, researchers caution that it remains unclear if ART itself, fertility drugs, underlying infertility of the parents, or other unknown factors may explain any increased cancer numbers among ART-conceived children. Overall, the incidence of cancer in children, regardless of conception method, is very low.

Gene therapy for profound genetic deafness has been advancing in recent years, with multiple clinical trials enabling hearing at normal levels for the first time without hearing aids or cochlear implants. The therapies target hearing loss caused by mutations in the OTOF gene that codes for a protein called otoferlin. That protein normally plays a key role in relaying sound signals in synaptic transmission between the ear's inner hair cells and the auditory nerve.